The present invention relates to a continuous process for making elastomeric star-block copolymers.
Highly branched block copolymers, sometimes called star-block copolymers, are old in the art of anionic polymerization. These star-block copolymers are prepared by first forming linear block polymer having active lithium atom on one end of the polymer chain. These active, linear polymer chains are then coupled by the addition of a polyfunctional compound having at least three reactive sites capable of reacting with the carbon to lithium bond on the polymer chains to add the polymer chain onto the functional groups of the compound.
Zelinski, U.S. Pat. No. 3,280,084, polymerized butadiene with butyllithium initiator to form B-Li blocks (where B is polybutadiene) which when coupled with 0.02 to 1 part by weight per 100 parts of monomers of divinylbenzene gave star-block copolymers having polydivinylbenzene nuclei and several identical arms of polybutadiene branching therefrom. The arms can also be either random or block copolymers of styrene and butadiene (from A-B-Li blocks, where A is polystyrene segment) where the diene is the major component.
Zelinski, U.S. Pat. No. 3,281,383, teaches similar star-block copolymers to those in U.S. Pat. No. 3,280,084, except that coupling agents such as polyepoxy compounds, polyacids, polyaldehydes, etc., are used.
Childers, U.S. Pat. No. 3,637,554, prepares rubber star-block copolymers having nuclei formed from polyepoxides, polyisocyanates, polyimines, etc., and identical arms from B-Li and A-B-Li.
Fetters et al, U.S. Pat. No. 3,985,830, discloses a product having a nucleus of more than one molecule of m-divinylbenzene and at least three polymeric arms, each being a block copolymer of conjugated diene and monovinyl aromatic monomers wherein said conjugated diene block is linked to said nucleus.
The above patents all suffer from the disadvantage of being lengthy batch processes which require cleaning out of the batch reactor after each run.
Brady et al, U.S. Pat. No. 4,209,599, discloses a process for the continuous mass polymerization of monomers in the presence of free-radical initiators in a tubular reactor provided with internal static mixers. The process requires the tubular reactor also to be a loop reactor to allow for recirculation of the reaction mass to the reactor as feed. This recirculating reactor is not suitable for the preparation of block copolymers.